My query is slow when ever I select inside concat or group_concat and I want to return them in form of JSON. how can I make it faster?

Question

I have a discount table (productdiscounts) where I inserted product ID and the accounts that I wish to give discount. eg all users under ABC account should be given a discount of 10% and users under account XZS should be given a discount of 90%, etc.

secondly I selected all the available accounts and the discounts associated to them as alldiscounts for staff to see which accounts have discount on a product.

 SELECT 
      products.manufacturer as manufacturerID, stock.expiryDate,
      *coalesce((select discount from productdiscounts where(productID=products.id and branchID=? and isActive='1' and patients.billingAccounts like concat('%\"',productdiscounts.accountID,'\"%')) order by discount desc limit 1),0.00) as discount*,
     **concat('[',(select 
    group_concat('{\"productID\":\"',productdiscounts.productID,'\",\"accountID\":\"',productdiscounts.accountID,'\",\"discount\":\"',productdiscounts.discount,'\",\"accountName\":\"',accounts.name,'\",\"accountNo\":\"',accounts.accountNo,'\"}') from productdiscounts 
    left join accounts on(productdiscounts.accountID=accounts.id)
    where(productdiscounts.productID=products.id and productdiscounts.branchID = ? and productdiscounts.isActive = '1' )),']') as allDiscounts**
    from products 

Answer 1

and  patients.billingAccounts like concat('%\"',productdiscounts.accountID,
                                        '\"%')

Is that fishing around in a JSON string? Can't you supply the whole accountID so you don't have to do the slow LIKE with a leading wild card?

With = instead of LIKE , this might help the first subquery:

INDEX(branchID, isActive, productID, AccountID, discount)

It might be more practical to do

 SELECT COALESCE(MAX(discount), 0) ...

instead of the ORDER BY discount DESC LIMIT 1 .

The other parts may benefit from

patients:  INDEX(billingAccounts)
productdiscounts:  INDEX(accountID)

Please provide SHOW CREATE TABLE and EXPLAIN SELECT...